U.S. Pat. No. 3,417,635 issued Dec. 24, 1968 to R. R. Day, et al discloses a single shaft control lever mounted on a steering column for swinging movement parallel to the steering wheel between forward and reverse positions, and for rotation about its own axis to change the speed ranges. The control lever is adapted to displace two spool valves through the two linkage mechanisms. U.S. Pat. No. 4,541,497 issued Sept. 17, 1985 to C. W. Riediger, et al shows another control mechanism using a laterally extending tiller arm swingably mounted on a fixed upstanding axis between a forwardly located position steering the vehicle in one direction and a rearwardly located position steering the vehicle in the other direction. A handgrip portion on the tiller arm can be revolved around its own axis to change the direction of the vehicle. In this instance, a separate speed lever was used to control the speed steps of the transmission, and separate mechanical linkages were used to couple the tiller arm, handgrip portion and speed lever to the remotely located spool valves. U.S. Pat. Nos. 3,417,635 and 4,541,497 are generally illustrative of the widely used, but relatively complex and costly mechanical linkage systems for connecting the operator controls to a remotely located transmission. Although generally successful, such mechanical linkage systems are difficult to assemble, disassemble and adjust. Moreover, because the location of the operator controls and the transmission varies from vehicle to vehicle, separate linkage mechanisms must be provided for each one. Accordingly, one of the objects of the present invention is to provide a reliable, and yet economical, electrically actuated transmission control mechanism that could have universal adaptability to a wide variety of applications.
U.S. Pat. No. 3,138,966 issued June 30, 1964 to D. D. Kempf, et al discloses a transmission control mechanism utilizing a plurality of microswitches disposed in fixed positions and actuated by a cam. These microswitches take up considerable space and are relatively expensive because they have resilient metal arms that are deflected continually over a long service period and are constructed to resist fatigue failure. Moreover, each one of the solenoids actuated by that control mechanism has the usual continually grounded line associated therewith. This is a disadvantage in that any inadvertent short in the wires or elements serially connected to the electrical power supply line leading to a single one of these solenoids could cause an unexpected movement of the vehicle. For example, with the engine running and the transmission placed in neutral, the control members might be jarred or bumped with a tool during a service check such that electrical power is communicated to just one of the solenoids through an unexpected short. While this is unlikely, it is conceivable--especially with older and dirtier mechanisms.
One desirable alternative to deflectable arm type microswitches is illustrated in U.S. Pat. No. 4,158,404, issued June 19, 1979 to S. Yamashita, et al. This patent illustrates a rotary switching device utilizing a rotatable member supporting a plurality of radially oriented contact elements which are resiliently biased toward a stationary member supporting sets of arcuately arranged contact members. With the actuation of a remotely disposed gearshift lever, the contact elements are rotated so they selectively wipe across or bridge the contact members and energize a single solenoid operated valve actuator for an input clutch. While this type of rotary switching device is desirable from the standpoint of compactness, reliability and low cost it is not efficiently utilized, and that apparatus still relies on the direct mechanical movement of a plurality of synchronizers for shifting the transmission itself. U.S. Pat. No. 4,745,826, issued May 24, 1988 to S. Nishikawa, et al also discloses this desirable type of switching device for a transfer gear mechanism in order to provide two wheel and four wheel high speed drive and four wheel low speed drive. However, that mechanism requires a complicated electronic control unit, does not locate and efficiently integrate the switching device at a desirable location immediately adjacent the operators hand control, and does not include an electrical system in conjunction with the switching device that would provide the desired degree of reliability and service life of the mechanism.
Thus, what is needed is an electrical transmission control mechanism using an easily operated and compact control assembly containing one or more reliable rotary switching devices therein immediately adjacent the operators hand. The control assembly should require minimal effort to shift it between the various operating positions thereof, and should incorporate appropriate detent means to enable the individual positions to be easily and positively selected. Moreover, the control assembly should preferably be constructed primarily of electrically nonconductive materials such as lightweight, rugged plastics and be positively sealed to exclude dirt and moisture from the electrical portion of the circuitry contained within it. And, still further, the control assembly and electrical circuitry used therewith should be adaptable to a wide spectrum of control assembly shift patterns and vehicle variations, and should preferably be adaptable to positively control both sides or leads of the solenoids being manipulated during the shifting process.
The present invention is directed to overcoming one or more of the problems as set forth above.